Didn't they fire converted HAFRs?
Uh, you know it doesn't say. There is every implication that it is infact the Mk 105s you have here.
I suspect it might be the unpowered single Army mount, but it could be the L70.
The A. D. Baker drawing shows it to be a twin (I have the drawing infront of me). I think that in the resize of the source several close lines greyed out and make it hard to visualize.
That said, I think they 40mm Bofors does match up well: